It is typical for thermometers and thermal switches to be calibrated using a drywell. Drywells may include a receiver in which a thermometer or thermal switch is inserted. A heating element and temperature sensor are in thermal contact with the receiver such that the temperature within the receiver may be accurately set. The set temperature of the drywell may then be compared to the readout temperature of the thermometer or the switching temperature of a thermal switch to determine its accuracy. In some uses, a reference thermometer is inserted within the receiver along with the thermometer or switch being calibrated, and the readout of the reference thermometer is used for calibration purposes.
In prior systems thermal switches were tested by inputting to the drywell controller upper and lower boundaries of a range that contained the nominal switch temperature. The drywell controller then swept the receiver temperature within that range in order to cause the switch to change state.
This method has a number of deficiencies. It requires a large amount of user interaction to determine and input the range. In some instances device specifications must be consulted or calculations made. Alternatively, the values used for the upper and lower boundaries of the range may be left to the guesswork of the operator. In some instances, the range input may potentially fail to contain the actual switching temperature of the switch or the upper or lower bounds of the switch's hysteresis range. The measured switching temperature may also be inaccurate due to variations in the rate at which the temperature is swept during testing, inasmuch as the thermal response time of the drywell and switch is not immediate.
In view of the foregoing it would be an advancement in the art to provide a convenient and accurate method for testing thermal switches using a drywell.